The measurement of a refractive index is expected to be applied in various fields such as agriculture, chemistry, biology, biotechnology, and medicine. As technology for measuring the refractive index, a measuring device and a measuring method of the refractive index using waveguide mode resonance and surface plasmon resonance are described in Patent Literatures 1 to 3.
A refractive index meter that acquires a refractive index of a sample easily with high accuracy is described in Patent Literature 1. When the refractive index is measured using the refractive index meter, measurement light is introduced into an end face of a waveguide layer of a waveguide mode resonance filter and emission light diffracted by a grating of the waveguide mode resonance filter at this time is detected by a light detector. An emission angle of the measurement light is scanned in a predetermined angle range by moving a position of the detector. As a result, a resonance emission angle corresponding to the refractive index is acquired.
A surface plasmon resonance sensor chip that has a diffraction grating and is suitable for miniaturization is described in Patent Literature 2. The diffraction grating is formed on an elastic film to be elastically deformable. When a refractive index is measured using the chip, light is incident on the diffraction grating in a state in which a sample is disposed in the vicinity of a diffraction grating surface. In a conventional surface plasmon resonance sensor chip, the intensity of diffraction light is measured by scanning an incidence angle of the incidence light. Meanwhile, in the chip, a resonance pitch corresponding to the refractive index is acquired by expanding the elastic film and changing a grating pitch of the diffraction grating surface dynamically, instead of scanning the incidence angle of the incidence light.
A surface plasmon resonance sensor is described in Patent Literature 3. The sensor has a waveguide core layer on which light for measurement is incident, a metal thin film, a dielectric film, and a sample layer to provide a sample for measurement formed on the dielectric film. When a refractive index is measured using the sensor, the sample is provided on the sample layer, light is caused to be incident on the waveguide core layer, and a wavelength spectrum or an incidence angle spectrum of the light transmitting the waveguide core layer is measured.